Radiation Disaster Associated Toxicity: Acute radiation syndrome (ARS) is a collection of health effects that are present within 24 hours of exposure to high doses of ionizing radiation. It is also called radiation poisoning, radiation sickness and radiation toxicity.

The onset and type of symptoms depends on the amount of radiation exposure, both in any one dose, and cumulative exposure. Relatively smaller doses result in gastrointestinal effects, such as nausea and vomiting, and symptoms related to falling blood counts, and predisposition to infection and bleeding. Relatively larger doses can result in neurological effects, including but not limited to seizures, tremors, lethargy, and rapid death. Treatment of acute radiation syndrome is generally supportive with blood transfusions and antibiotics, with some extreme cases requiring more aggressive treatments, such as bone marrow transfusions.

The radiation causes cellular degradation due to damage to DNA and other key molecular structures within the cells in various tissues. This destruction, particularly because it affects the ability of cells to divide normally, in turn causes the symptoms. The symptoms can begin within one or two hours and may last for several months. The terms refer to acute medical problems rather than ones that develop after a prolonged period.

Similar symptoms may appear months to years after exposure as chronic radiation syndrome when the dose rate is too low to cause the acute form. Radiation exposure can also increase the probability of developing some other diseases, mainly different types of cancers. These later-developing diseases are sometimes also described as radiation sickness, but they are never included in the term acute radiation syndrome.